Data may be transmitted as a sub-carrier in the lower vestigial sideband (VSB) spectral region of a standard television signal, e.g., a National Television Standards Committee (NTSC) broadcast video signal. Normally the standard television signal is generated by double sideband modulating a radio frequency (RF) or an intermediate frequency (IF) picture carrier with a baseband composite video signal and thereafter vestigial filtering the modulated signal to remove the majority of the lower sideband. The vestigial sideband, which nominally extends to 1.25 MHz below the picture carrier, contains low frequency luminance information. This low frequency luminance information within the vestigial sideband is duplicated by low frequency luminance information within the television signal extending from the picture carrier to 1.25 MHz above the picture carrier. It has been determined that a portion of the luminance information in the vestigial sideband may be replaced with auxiliary digital audio information or other information without significantly affecting the video signal recovered by a receiver. The other information may comprise e.g., a quadrature phase shift keying (QPSK) modulated data signal.
K. Jonnalagadda, in U.S. Pat. No. 5,029,003, discloses an apparatus for removing video signal from a portion of the vestigial sideband of a television signal and inserting a digital audio signal therein. Also disclosed is a receiver for recovering the digital audio signal from the television signal. The receiver contains standard picture processing circuitry including a video intermediate frequency (IF) circuit and standard sound processing circuitry including an audio IF circuit. The receiver also includes an auxiliary data processing circuit, including an auxiliary IF circuit, bandpass filter and digital demodulator for recovering the digital sound signal.
Unfortunately, the receiver disclosed in U.S. Pat. No. 5,029,003 requires an inordinate amount of circuitry to extract data from the vestigial sideband of a television signal.
Therefore, it is seen to be desirable to provide a receiver having the capability of retrieving data which has been transmitted as a sub-carrier in the lower VSB spectrum region of a data carrier without utilizing an inordinate amount of circuitry. Specifically, it is seen to be desirable to provide a television receiver which does not require an auxiliary IF circuit to recover data from the VSB region of a television signal.